This invention relates generally to ceramic insulation and, more particularly, to rigidized refractory fibrous ceramic insulation for use in aerospace systems and a method for manufacturing such insulation.
Various components of aerospace systems may be exposed to elevated service temperatures or large temperature gradients which require that they be insulated. Ceramic insulation has therefore been applied to aircraft engine and engine exhaust components such as nose cones, firewalls and exhaust ducts to protect them from hot exhaust gases. Ceramic insulation has also been applied to the outer surface components of space vehicles as protection against the elevated temperatures and significant temperature gradients experienced upon takeoff and reentry.
Bendig, U.S. Pat. No. 5,041,321, describes a method of making fiberformed ceramic insulation by forming a slurry of ceramic fibers, molding the slurry to form a soft felt mat, drying the mat, and incrementally introducing a sol into the mat which is gelled to form a rigid mat. The incremental addition of the sol is accomplished through a multiple impregnation technique in which a small amount of sol is initially infiltrated into the mat, is gelled, and is cured to stabilize the mat dimensionally. Stabilizing allows handling and further processing of the mat. The mat is thereafter strengthened to its final form by successive additions sol which is gelled and cured. This technique cures the mat to a rigid shape without appreciable shrinking of the resultant structure. Density of the final product can be controlled with successive additions.
Despite its many advantages, the method disclosed in Bendig, U.S. Pat. No. 5,041,321, has reproduceability problems when the goal is to produce relatively thick insulation having uniform structure and density. To be practical, this thick insulation should be relatively free of cracks.